The present invention relates to fuel injection control systems for internal combustion engines, and more particularly to a fuel injection system for diesel engines which controls the amount of fuel injected from a fuel injection pump into each cylinder by electronically controlling the opening and closing of a valve provided in a spill port communicating with a low pressure chamber defined in the fuel injection pump.
As one of devices for performing fuel injection into an internal combustion engine such as a motor vehicle diesel engine in accordance with the engine operating conditions is well known a spill type fuel injection device wherein the termination of fuel injection is effected by spilling fuel compressed for the injection into each cylinder of the engine. The spill type fuel injection device, as being illustrated in Japanese Patent Publication No. 51-34936, generally comprises a cam rotated in synchronism with rotation of the internal combustion engine, a fuel injection pump having a fuel-compressing plunger reciprocated in accordance with the rotation of the cam, a detector for detecting a reference rotational angle position established in corresponding relation to the vicinity of bottom dead center of the plunger and generating a signal in repsonse to the detection, and a solenoid-operated valve for performing the opening and closing of a spill port establishing communication between a pump chamber of the fuel injection pump and a low-pressure chamber defined in the fuel injection pump. The opening timing of the solenoid-operated valve is controlled by a control unit in which the duration for fuel injection is calculated on the basis of the engine operating conditions and a control signal indicative of the opening of the solenoid-operated valve is generated at the time elapsed by the calculated duration from the time of the generation of a detection signal from the reference rotational angle position detector.
However, such a fuel injection device provides problems in that: (1) a response time lag is occurred between the generation of a control signal indicative of the opening of the solenoid-operated valve and the actual opening thereof and the response time lag assumes a diferent value for each of fuel injection devices; and (2) an error of generation timing of the detection signal is caused by the fitting error of the reference rotational angle position detector occurred on manufacturing and the fitting error varies widely. These problems result in variations or dispersion of fuel injection amount although engines are respectively in the same operating condition.